Direct part marketing (DPM) produces a machine and/or human readable marking directly on a part or product where alternative the marking techniques are difficult, not possible, or not practical. As understood in the art, DPM is often used for quality, identification, inspection, safety, and other reasons. Marking metal parts, such as automobile or machinery parts, may lend themselves best to DPM as stickers or other markings may interfere or fall off during an assembly process.
As another example, medicines, such as pills, may also lend themselves best to DPM as there are basically no alternatives due to size and shape of the medicines.
DPM can be performed using a number of techniques. One technique for performing DPM on metal parts is to use dot peen marking. Dot peen marking includes producing indentations on a surface of a part (see FIG. 2) with a pneumatically or electromechanical driven pin or stylus. The dot size and imaging appearance are determined mostly by the stylus cone angle, marking force, material hardness, and illuminator used when imaging. The readability of dot peen marked symbols depends strongly on the resulting shape, size, and spacing of the dot and also by reflections due to an illuminator. In production lines, imaging the parts to identify DPMs on parts can be challenging due to speed and imaging quality specifications and requirements.
Existing systems that read DPM codes use certain 2D imaging processes and 3D imaging processes, including laser displacement imaging, laser triangulation imaging, time-of-flight (TOF) sensing, image differencing, and other imaging and image processing techniques. These imaging and image processing techniques, however, have various shortcomings due to reflections, loss of color, loss of other physical characteristics, and other shortcomings that cause DPM reading to be difficult to use in practice.